ACTUATION BEHAVIORS OF FLEXOELECTRIC AND LIGHT-ACTIVATED SHAPE MEMORY POLYMER ON RINGS

Some vibration problems caused by the low stiffness and light weight of large aerospace structures hinder precision operation. To enhance the environmental adaptability of the structure and improve its performance of the structure, sensors, actuators, and controllers are integrated with the structure, and signal processing and electronic circuit systems are combined to form a smart structure system. Smart materials and structures usually exhibit multi-field coupling behavior. Among them, flexoelectric materials have gradient coupling characteristics, that is, the linear coupling between electric polarization and strain gradient and between polarization gradient and strain. Flexoelectric materials are more sensitive to changes in bending strain or structural curvature. Therefore, the flexoelectric actuator is very important for controlling the deformation and vibration of the bending structure. A light-activated shape memory polymer (LaSMP) exhibits coupling behavior. Under ultraviolet (UV) light illumination, the Young's modulus of LaSMP changes greatly and the material returns to the initial state. Based on its shape memory properties, LaSMP actuators can be used to actuate and control thin shell structures. Ring structure can be applied to torpedo, missile and underwater vehicle shell joints, etc. In this work, an atomic force microscope (AFM) probe is placed on the top of a flexoelectric patch to induce an inhomogeneous electric field. A LaSMP has dynamic Young's modulus and strain under the illumination of UV lights. Therefore, both the flexoelectric actuator and LaSMP actuator can be used to actuate structures. This work aims to study the actuation behavior of the flexoelectric and LaSMP actuators on rings. The membrane forces and bending control moments and their induced components are defined respectively in the transverse/circumferential directions. In case studies, the circumferential distribution of the induced membrane force and bending control moment is analyzed first. The membrane force induced component and the bending control moment induced component, together with the total effect, are studied. Then, the induced microscopic transverse/circumferential actuation behavior is evaluated. Finally, the effects of bending and membrane of the flexoelectric actuator are compared. The results suggest: (a) the membrane force and bending control moment induced by the flexoelectric actuator concentrate near the AFM probe location, while the membrane force and bending control moment induced by the LaSMP actuator distributes throughout the LaSMP patch; (b) the overall actuation behavior of the flexoelectric actuator can be regarded as a drastic sharp bending effect near AFM probe location; and (c) the LaSMP actuator shrinks in the circumferential direction under UV light.